<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>

        div {
            /*标签选择器优先级较低*/
            color: blue;
            font-size: 40px;
            /*width: 500px;*/
            /*height: 100px;*/
            border: 1px solid red;
        }

        #div3, #div1, #span2 {
            /*多个选择器的连接之一*/
            color: green;
            background-color: red;
            /*border:三个值，分别是边界线宽度 边界样式 边界颜色*/
            border: 1px solid black;
        }
    </style>
</head>
<body>
<div id="div1">div标签1</div>
<div>div标签2</div>
<div id="div3">div标签3</div>
<span>span标签1</span>
<span id="span2">span标签2</span>
<span>span标签3</span>
</body>
</html>